A Fragile and Unique Eco-system – Siju cave

Mother Nature has blessed the state of Meghalaya like no other although many of us hardly appreciate this fact. Be it scenic beauty, biological diversity or geological wealth, everything is in abundance in the state. Meghalaya holds some of the richest karst landscape in the Indian Subcontinent which was formed due to dissolution of limestone through the action of water. As a result, the state is dotted with numerous caves and sinkholes of which about a thousand have been scientifically explored and mapped. 

Caves are defined as “any cavity in the ground that has a section which does not receive direct sunlight”. Thanks to the efforts of Meghalaya Adventures Association led group of multinational cave explorers, Meghalaya has earned a prominent place in the caving map of the world attracting the attention of explorers and biologists alike. The Siju Dabakhol (cave in Garo parlance) is one such cave located in South Garo Hills of the state which so far holds the distinction of the best explored cave in India, as far as cave fauna is concerned. 

Although the cave has been known to the local populace for centuries, it was Mr. T. D. La Touche, famous geologist of Geological Survey of India who led the first geological investigations into the cave in 1881 and also mentioned about huge colonies of bats residing in the cave. In 1922, a team of zoologists led by Dr Stanley Camp and B. Chopra of Zoological Survey of India (ZSI), Kolkata conducted a three weeks intensive faunal exploration of the cave. The results of the explorations were published as a series of papers subsequently which recorded the presence of 102 animal species including several species new to science, like a cave dwelling shrimp and a snail species. This exploration remains a landmark event in the history of biospeleology (study of cave fauna) of India and to date remains the most authoritative biological explorations of any Indian cave. Although there have been a few intermittent surveys, the only published work pertaining to the fauna of Siju cave includes a study on the bat fauna of the cave by ZSI, Shillong in the late nineties, wherein presence of nine bat species from the cave was reported.   

After a gap of about a century, Zoological Survey of India, Shillong conducted a series of re-survey of the cave during the period of 2017-20. The objective of the surveys was to document the present faunal diversity in the cave and to record the changes in faunal composition over the period of 100 years or so. It is to be emphasised here that the scientific rigors of the previous survey in 1922 remains unmatched as the explorers spent days together inside the cave, meticulously documenting the cave passage as well as fauna encountered. As part of the present survey team, this author also visited the cave twice during the dry winter seasons as the cave remains inaccessible during summer and most of the fall. These visits, on the other hand, were only daylong surveys but with better logistics; it was expected to document the current faunal status inside the cave to a satisfactory level.  

The details of the survey results are still being worked out although a decline in population size of many of the species recorded during the 1922 survey was clearly recorded. However, the results of an independent survey conducted by Dr. Dan Harris of Grampian Speleological Group, Edinburgh, in 2019 have recently been published in the Journal Cave and Karst Science. The publication which was co-authored by scientists from ZSI, Shillong including this author documented a relatively similar faunal composition and distribution inside the cave. But to the concern of cave biologists and conservationists, the study noted severe decline in abundance of bat populations and many species of invertebrates that were associated with bats. It may be noted that a cave system with its biota is a fragile and unique ecosystem which is very sensitive to outside disturbances. In an energy impoverished ecosystem like caves, bat guano constitutes an invaluable source of energy upon which a large variety of guanophilic animals (organism growing on animal excreta) thrive. These in turn serve as food source for several other species, thus enriching the cave biota. Therefore, this noted decline of bat population and associated guanophilic biota is a serious cause of concern. 

Another important finding from this study is the report of abundant occurrence of a cockroach species resembling troglomorphic dictyopteran, Typhloblatta caeca throughout the cave system which was not recorded during the 1922 survey. This cockroach species is a truly cave adapted species (lacks eyes and pigmentation) thus precluding the chance of a recent introduction. It was concluded that in all probability, this species was possibly present in inaccessible areas of the cave and hence was not recorded during 1922 surveys. 

Although Siju cave as a geologic system may not have changed in the past century, the environ around it has certainly changed a lot. To support tourism activities and thereby the local economy, it has been promoted as a tourist attraction. Although the pressure from tourism is not very high unlike other places in Meghalaya, a few tourist groups each day during the peak season is sufficient enough to disrupt the fragile ecology of the cave. Since many bat species (upon which the cave biota depends significantly) are prone to human disturbances, the reduced diversity and abundance of bats will certainly have negative consequence on other fauna as well. 

Besides, the natural vegetation around the cave has extensively been converted for agriculture activities especially for cash crops like Areca nut. This, in turn, might have negative effect on the bats species living in the cave as availability of fruits and insects in the nearby areas must have depleted considerably. While socio-economic development of the villagers is a crucial priority for the Government, a balance must be struck with conservation priorities. 

A natural heritage like Siju cave should not be promoted as a tourist destination as it has the potential to irreversibly damage the ecology. Instead, more emphasis may be given for development of water sports and related activities as relatively pristine river Simsang passes through the area. It is easier said than done, but hopefully an ecologically sustainable model for development of surrounding areas of Siju can be developed with the cumulative knowledge of experts and government goodwill. We hope so!  

All images courtesy the author

(The author is a scientist at Zoological Survey of India and can be reached at [email protected])

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